Ural 1966 Cycling Roads

#include<cstdio>
#include<cmath>
#include<iostream>
using namespace std;
#define maxn 205
struct point
{
    double x,y;
    point(double x = 0,double y = 0):x(x),y(y){}
}p[maxn];

struct Line
{
    point a,b;
    int pos1,pos2;
    Line(){}
    Line(point x,point y,int ppos1,int ppos2){  a = x; b = y; pos1 = ppos1; pos2 = ppos2;}
}line[maxn];

int n,m,cnt;
int par[maxn];
int c[maxn];

typedef point Vector;
Vector operator +(Vector A,Vector B){ return Vector(A.x+B.x, A.y+B.y);  }
Vector operator -(Vector A,Vector B) { return Vector(A.x-B.x,A.y-B.y);  }
Vector operator *(Vector A,double p) { return Vector(A.x*p,A.y*p);  }
Vector operator /(Vector A,double p){ return Vector(A.x/p,A.y/p);  }
const double eps = 1e-10;
int dcmp(double x)
{
    if(fabs(x) < eps) return 0;
    else return x < 0? -1:1;
}
bool operator == (const point &a,const point &b)
{
    return dcmp(a.x-b.x) == 0 && dcmp(a.y-b.y) == 0;
}
double dot(Vector A,Vector B){  return A.x*B.x + A.y*B.y;  }
double cross(Vector A,Vector B){ return A.x*B.y-A.y*B.x;  }

bool OnSegment(point p,Line l)
{
    return dcmp(cross(l.a-p,l.b-p)) == 0 && dcmp(dot(l.a-p,l.b-p)) < 0;
}
bool SegmentProperIntersection(Line l1,Line l2)
{
    point a1 = l1.a;
    point a2 = l1.b;
    point b1 = l2.a;
    point b2 = l2.b;
    double c1 = cross(a2-a1,b1-a1);
    double c2 = cross(a2-a1,b2-a1);
    double c3 = cross(b2-b1,a1-b1);
    double c4 = cross(b2-b1,a2-b1);
    return dcmp(c1)*dcmp(c2) < 0 && dcmp(c3)*dcmp(c4) < 0;
}

void init()
{
    for(int i = 1; i <= n; i++)
        c[i] = 1;
    for(int i = 0; i < maxn;i++)
        par[i] = i;
}
int Find(int x)
{
    if(par[x] != x)
    {
        return par[x]=Find(par[x]);
    }
    else return x;
}

void Merge(int a,int b)
{
    int t1 = Find(a);
    int t2 = Find(b);
    if(t1 != t2)
    {
        par[t2] = t1;
        c[t1] += c[t2];
        //printf("%d %d   merge\n",a,b);
        //return 1;
    }
    //return 0;
}

void input()
{
    int x,y;

    for(int i = 1; i <= n; i++)
    {
        double x,y;
        scanf("%lf%lf",&x,&y);
        p[i] = point(x,y);
    }
    for(int i = 0; i < m; i++)
    {
        scanf("%d%d",&x,&y);
        line[i] = Line(p[x],p[y],x,y);
        for(int j = 1; j <= n; j++)
        {
            if(OnSegment(p[j],line[i])) Merge(j,x);
        }
        Merge(x,y);
    }
}

void deal()
{
    for(int i = 0; i < m; i++)
    {
        for(int j = i + 1; j < m; j++)
        {
            if(SegmentProperIntersection(line[i],line[j]))
            {
                Merge(line[j].pos1,line[i].pos1);
                //Merge(line[j].pos2,line[i].pos1);
            }
        }
    }

}


int main()
{
    //freopen("input.txt","r",stdin);
    while(scanf("%d%d",&n,&m) == 2)
    {
        init();
        input();
        deal();
        if(c[Find(1)] == n) printf("YES\n");
        else printf("NO\n");
    }

    return 0;
}